1. Field of the Invention
This invention relates to the deposition of thin films of metal on substrates.
2. Prior Art
Vapor deposition of thin films of material on substrates is known. Generally, a welding torch of the type used in GTAW welding is used as the energy source for deposition of the metal film. An inert gas, such as argon, is passed through the torch with an electrical current sufficient to ionize the gas and form a plasma stream which is applied to a target made of a metal which is to be coated onto a substrate. The torch is mounted inside a vacuum chamber.
The plasma stream melts a pool of the target metal and then vaporizes a portion of the molten pool. Because of the vacuum applied to the chamber, the vapor from the target material flows outward from the target and forms a film on the substrate.
In a conventional vapor deposition process, the torch is placed directly over the target metal, as illustrated in U.S. Pat. No. 5,380,415, and the plasma directed onto the target metal, with the substrate to be coated being positioned to one side of the target. The disadvantage of this process is that the vapor flows outwardly from the target in all directions. While this might be the best method for coating the inside of a ring or cylinder, it does not work so well for other substrates.